The assignee of the present invention designs and manufactures spacecraft for, inter alia, a variety of services from geosynchronous orbit. Some payloads of such spacecraft have temperature-sensitive components with stringent thermal requirements. By way of example, an infrared imager of a spacecraft that includes a meteorological payload may require to be maintained at cryogenic temperatures in order to reduce noise in image production. Referring to FIG. 1A, a 3-axis stabilized spacecraft 100 may be regarded as including a main body 110 enclosed by sidewalls facing, respectively in a north, south, east, west, Earth (nadir) and anti-Earth (zenith) direction. When the 3-axis stabilized spacecraft is operating on-orbit, an earth facing imager 120 may be thermally coupled with a north (or south) facing radiator 125. As a result of being oriented to face north (or south) the radiator 125 has limited exposure to the Sun and may efficiently radiate heat into space. Nevertheless, the radiator is exposed to seasonally and diurnally varying thermal loads from the Sun and/or backload from solar arrays of the spacecraft, which may result in higher than desired temperatures.
In a conventional spacecraft, exposure of a temperature-sensitive component to solar radiation and/or backload from solar arrays may be reduced by a seasonal yaw flip strategy, e.g., twice per year flipping the spacecraft 180 degrees, such that radiator exposure to direct solar loads is avoided. The yaw flip strategy may cause the radiator to be north facing from late September to late March (from the autumnal equinox to the vernal equinox) and cause the radiator to be south facing from late March to late September (from the vernal equinox to the autumnal equinox). However, a seasonal yaw flip strategy is not acceptable for many payloads because placement of many components, such as antennae, is often asymmetrical. Therefore, yaw flip may result in unacceptable changes to antenna coverage patterns on the ground.
To avoid thermal backload from a solar array onto the radiator of meteorological payloads, some conventional spacecraft, e.g., as spacecraft 150 of FIG. 1B, have avoided disposing a solar array in view of a radiator, e.g., radiator 154 of the spacecraft 150. For example, the spacecraft 150 includes a specially designed solar sail 152 that has been provided in lieu of an omitted solar array to provide balanced solar torque. The solar sail 152 can be sized and placed to balance the torque arising from solar pressure on the single solar array 156. However, the solar sail 152 adds deadweight to the spacecraft 150 without providing any added capabilities.
Accordingly, in the absence of the present teachings, spacecraft carrying payloads having temperature-sensitive components must often be built with significant design constraints.